Is this all just friendly, or am I being paranoid?

[Theyu4]

I have a work colleague (London/banking) who has become very close with me over the years. I can’t work out if he’s genuinely nice to me for no reason or if there’s more to it. Perhaps my judgement is clouded by the fact that many “friendly men” in my career ended up making a move on me, etc.
He has been a lifesaver at work. We support each other; he helps me, and I help him. He’s always there for me.
But I can’t shake the feeling there’s more in it: for instance, I have another senior member of the department commenting on our close relationship, he comes to my desk a lot to chat, he calls me on the pretext of work and can easily talk for 40 mins, he compliments me on my work performance, he told me a lot of deeply personal things. But equally, we never text outside work hours, and he never said anything inappropriate. The thing is that he’s not like this with others at all at work. Lately, he’s been involving me in his projects and client meetings when that’s not essential.
The other day, he came to my desk and said, "I saw you smiling, and you looked happy, so I wanted to say I am glad you are." Maybe this could be acceptable for an extroverted individual but not for a 50-something introverted married man.

Should I lean in and let him be there for me or keep my guard up? Maybe my past experiences are clouding my judgment.

For context, we are both at the same level at work.

He's married,I wouldn't encourage him. If he leaves his wife that's a different story. If his intentions are to have an affair with you ask yourself if you want a man who cheats. The more you engage with him the more he is going to push the boundaries of what should be a working relationship. Does his wife know how 'close' you are? If your worried just back off but you have to want to do that. It takes two to tango.

There is no interest on my end in an affair or anyone leaving anyone.

It feels all controlled, as we only see each other in the office occasionally; there are certainly no meetings after work or over the weekends. He is very supportive at work and will go out of his way to help me if I ask for his opinion. But he calls a lot now, and those calls are getting longer, although again centred around work issues; I noticed he says to contact me anytime/I know it’s hard/and I feel angry on your behalf/I can support you on it. I have other close friends at work, but none would call for an hour chat. It’s not that kind of place.

Gosh, is this still going on? Just nip it in the bud already and distance yourself. It won't end well.

It’s been like this for years…

Head in the sand springs to mind OP. Are you not embarrassed to be engaging so closely with this married man. He would never be on the phone to you for an hour unless you were engaging in the conversation. What's wrong with thanks for calling .... appropriate excuse....I'll speak to you later. He'd soon get the message.

There's nothing confusing here. If this was a straightforward case of two colleagues work well together and have a platonic personal connection you wouldn't feel the need to post about it. The fact you have made this post means you know full well there is more to this relationship than that.

I don't know if the unacknowledged sexual attraction is only on his side or if you reciprocate it but it's faux-naive to pretend that it doesn't exist.

No, don't lean in to this. Your 'friend' has feelings for you. He is married and those feelings will be threatening his marriage. Just because he doesn't message you out of work, he's not switching off that level of interest, he's thinking of you when he should be present in his family. As people at work have noticed, he is also making a fool of himself, and by extension his 'poor wife' who has become the stereotype of the unsuspecting spouse who's husband sniffs round a younger woman. By leaning in you will be encouraging his foolishness and exacerbating the risk to his marriage. And while that's not your responsibility, I'm sure you'd rather not add to harm if you could help it.
Also from pure self interest, you are unlikely to come out unscathed. Its highly likely your 'friend' will escalate (he is already) and will either declare feelings, or worse make a physical move. This could put you at best in a very awkward situation (his career will not be the casualty) at worst at risk. You need to distance yourself and give no encouragement at all to the personal stuff. If he oversteps you need to telk him straight that it needs to stay professional. Good luck. When senior men do this, it takes some navigating.

I agree with this but honestly can’t help suspecting the sexual interest isn’t MORE on op’s side. No one obsesses like this over a platonic dynamic - and it isn’t him posting…

Thank you, everyone, for your comments. This situation was getting a bit too much for me, so I decided to withdraw from it and become more reserved with him. I think a bit more professional boundaries are needed here, and while I still respect him and appreciate his support, it’s for the best to make it much more professional.

@Theyuu4 I don't think your original name has been used. I agree with your decision, you don't need to know what's going on in his head to know that keeping things professional and boundaries very strong will benefit you and your career. I've had to do this before and it's just easier once things are very clear from your end- no need to take nice long lunches with him spilling out his problems, people will not say anything about the 'two' of you- on your part it may have just been a friendship and mentorship, it's better to keep it that way.