Thank you all for the responses, it really helps to get some perspective from people who have gone through similar experiences.
I think I’m starting to see the situation a little clearer rather than feel I’m the unreasonable one for needing honest communication about this. The problem is I don’t think I will ever get it since everything I know I have either had to confront him over with evidence or find out through drunken admissions. 
I don’t want to spend my life with a man who thinks it was ok to hook up with men for secret sex and then come home to ex girlfriends with a clear conscience.  I can’t live my life wondering about this.
I just hope I can find the strength to make the break from him, as I do deeply love him.. the others on here who have been brave and strong enough to take that step are an inspiration.

I’m new to the forum but have been reading posts on here for around 6 months.
Around 3 years ago I started dating an old boyfriend who had been my first love when we we 20 and 30 years old. I’m now 38 and he’s 48, we got back together and it was amazing- both felt we had our soul mate back.
18 months ago whilst on holiday and feeling very in love he told me one night that he was 5% bisexual and prior to getting back together with me had been meeting up with a gay man for sex only for 4 years on and off.   All the while he had had girlfriends and told himself it wasn’t cheating as it was not with a female. Also because it was so secretive he could actually live the double life comfortably and did not feel like it was hurting anyone.
He said he had decided to tell me because I’m the love of his life and his one true love and he wanted to be open and honest about his past without this secret, which he had stopped as soon as he started dating me.
He said he was still in touch with the man but only to say hello occasionally by text and swore there had not been any meetings, which I believed due to his telling me in the first place.
After the initial shock I became angry and demanded we went and got tested for STIs as soon as we got home from our holiday. He begged and swore to me that he had never put me at risk and had always been 100% safe, used condoms, and that I was  over reacting. I had to drag him to the clinic with him trailing paces behind me due to his fear of seeing someone he knew!
Anyway all came back clear, but in my mind a few things he had said didn’t add up, and to cut to the chase I went through his phone one night (hate myself for doing so and felt terrible for it) when he was passed out drunk and found messages from a second man around the time we got back together with the man asking to meet him for a good ‘f****’ and my boyfriend had replied saying ‘sorry I’ve stopped all that now as I’m with a girl I really care about’.