Depression or just waking up to my real feelings?

[firewalkeruk]

My DW and I have been together for just over 36 years now. I was 19 when we met and she was 27 with two sons and still married at the time.
I'm not saying I'm any innocent but when we first met I didn't know she was married and by the time I found out I was head over heels in love with her.
I had had girlfriends before, all short term, and I was still a virgin until I met my wife.
Over the years things have been turbulent and we struggled financially for a very long time but we coped and nobody ever went hungry or cold.
We had a son who joined his two brothers and I always treated the boys equally, they are all my sons and I love them all.
I'm not going to go into detail but my wife had an affair which almost broke us up and a dalliance with a friend of our oldest son which she cut off when she realised that her feelings weren't really for him but she was unsure if she still loved me.
For the last 20 years she has been a faithful and loving wife and she has even said that I have been the most stable thing in her life and that she can never forgive herself for hurting me.
I can be hard to live with and would say I have a tendency to bi-polar behaviour which is hard on those around me.
My wife suffers from severe depression and several social anxiety issues for which she gets treatment but there is an effect on out life, she is OCD and our home has to be kept in a certain way or she gets very upset. Add to this the Covid thing and the world is terrifying for her.
Over the last two years I have felt very criticised and can never seem to get anything right no matter how hard I try.
Due to illness I am very obese and our sex life is practically nonexistent, perhaps 3 or 4 times this year. I am not blaming my wife for this but I don't feel encouraged by her and I suppose my self confidence is lacking.
If I am honest I haven't been happy for the last two years and feel I am only holding on out of loyalty.
I fear that if I leave my wife she couldn't cope and might do something to harm herself and to be honest I fear spending the rest of my life alone.
Is it right to cling on to a relationship out of a sense of duty and a fear of the future?
I have been happy with my wife and do love her but I'm not sure getting by is enough.
There is no one else before anyone asks, it has always been my wife and I have never really had feeling for other women.

Is it right to cling on to a relationship out of a sense of duty
NO!
I split with my ExH because he was going to stay out of 'duty' to myself and my DD.
When he said those words, that was the end for me.
I did not want anyone to be with me out of 'duty'.
Love, respect, etc.... yet. DUTY - NO!!!
But... you say you love her.
Can you imagine your life without her?
Could you go to therapy together to try to unpick this and see if there is anything worth saving?
Might be a good place to start.

You were very young when she got together with you and she was considerably older. She also had a thing with her son's friend?? She sounds a bit predatory

Hellsbellsmellons, I have never doubted that I love my wife and I am wise enough to know that there is very little difference between being in love and loving someone.
There are times that I feel that first flush of desire, I catch myself looking at her when we are out or with family and see her almost like I did the first night we met. There are other times when it feels more like best friends hanging out.
Perhaps what I am feeling is the loss of the infatuation I first felt for her. Growing old doesn't mean we stop wanting to be excited about being with someone.

I can’t get past the fact she had a “dalliance” with her sons friend?! 100% agree with @Sakurami- she sounds predatory. This alone would be enough for me to walk away OP.

Ladies just so we don't get fixated on this our son was 27 at the time, his friend 35 son not quite a child.