Worried about boyfriend

Okay so I'm a 18yr old straight girl who has been in a relationship for over 2 years. So today I saw on my boyfriends phone that he had Grindr downloaded, and after clicking on it I discovered that he'd been messgaing people on there and had sent pics etc but all in a fake identity. When I confronted him about it he told me he was bi which obviously came as a bit of a shock to me but the fact he's bi is not a problem for me.

I asked him why he had never told me before and he said he was too scared of how I would react and that it would mean I would break up with him. However my main issue was why he was messaging other guys behind my back, his response to this question was 'I don't know, I just wanted to see how other people like me cope' He is adamant that he has never met up with anyone he's spoken and that he never would have done and was in absolute floods of tears telling me how much he loved me and that he was really sorry for what he'd done but just didn't know how to deal with it. He wanted to talk to people but didn't want it to be anyone he knew.

I still really love him and don't want to lose him but I am very concerned about the fact he's been messaging guys and felt the need to go on grindr rather than seek support from a helpline. I don't quite know what to do and was wondering if anyone had any advice or has been in a similar situation.