My oh of 7yrs is being underhand, possible cheating

[Emface]

A few months ago, my oh got a text that he swiftly deleted, though I saw it came from a girl. I asked why he deleted and he evaded the question and got really defensive. He has never given me reason to suspect him before and I wasn't being interrogative, just wondering what had happened.
I was just playing around on his phone looking at some of our messages when I saw he had resaved the number as an old female friend of his, but stupid boy had kept the strange girl's surname as part of the contact profile. He has deleted the message but as it's an iPhone I can see it is there from 6th June. He has blocked the girl on Facebook.
What do i do? Trouble is, 3 years ago, I fucked up big style as I had a huge wobble in our relationship (we have been together since I was 20) and fell for someone completely and had a short relationship with him. I tried to break up with my oh but he was so devastated we kind of ended up being on a break as I couldn't make the final split (I know this was unfair. I blame immaturity and wanting to stop his short term pain rather than thinking about the long term greater pain). He never brings it up and we have moved on, but the only time he did bring it up was when I asked about this strange text months ago. I know he will do the same if I ask again, plus he will wonder how I know about the new message and even though I was only messing around with his phone, it smacks of underhandedness.

What do I do? Can I speak to this girl? Or text from a new number? That sounds so conniving but I am being eaten up with not knowing. Can I tell him that I know what is going on rather than ask him? What should I do? W are planning on buying somewhere together next year; he really wants to get married but I admit that I am not the marrying kind.

I know that I have no right to be hurt and angry as I did the Same to him (probably worse) but the not knowing is horrible.

Sorry ended up being an essay.

Thanks for the post. Glad im not totally crazy for wanting to snoop. I'm afraid I wasn't honest - his friend told him whilst we were on a break. I was a coward who didn't want to hurt him. So I deserve this but I don't know how to talk to him. We talk about everything but this- we can't.

You're focusing on the wrong person i.e the girl. Your relationship is with your husband/partner not some random woman. Snooping achieves nothing. If you've been with him 7 years and you ask him a straight question you will know if he's being evasive or lying when he answers. Whether he's cheating or not, there's no future with someone you don't trust

Ask him about it. If you want different things, wrt marriage and other things, it may be time for a big talk.

They are two different conversations though. Him hiding things on his phone, and you both needing to know what you want out of the relationship.

What you did in the past is not relevant, you're still there and you both worked through it. Bringing up old slights won't help and will distract from the main issues , such as are you seeing or talking to someone else with a view to intimacy or have already dtd, and what are we doing together and are we making each other happy.