I don't know what to think...

So me and this lad has seeing each other for nearly 4 months now and we've been together 1 month, however, be has an extremely horrendous past that he's not proud of where he got drunk every night and was maki g out with tons of lasses even lasses he was speaking to but then making out with their best friends! He said he regrets it all and this time with me it's different having gone through that and realised he wants to settle down and he enjoys my company and stuff. We went out together for the first time Saturday and I thought he kissed someone but he said he didn't and obviously I was drunk and got myself upset. But then his mate told me he was with him the whole time and that he didn't do anything I hugged him and tod him I loved him for the first time which I meant. His mate then said to him 'I've got your back' like does this mean he did kiss someone and his mate is protecting him or that his mate is helpi g us out by telling me the truth? My boyfriend swore blind he didn't as he doesn't want to fuck things up and we're looking to move in a little flat in January. But I can't help but have this on my mimd😔 I was with him virtually all night but still there was times when we weren't together? I just don't want to be crazy and insane if I'm reading too much in to it