Advice needed!

My fiancé told me he messages others (both males and females) by using these random websites or dating apps. Sometimes it’s just to talk and others/mostly it’s used for sexting (NEVER does he meet up with anybody he’s talked to on these apps) He has no idea why he does it....like truly has no idea.... (it’s not like he’s unhappy or bored) He’s told me he can go from feeling no guilt at all about doing it to crying and feeling horrible about it. We’ve been together for over 4 years (being engaged for one) and he is literally my best friend. I don’t want this to make him look like he’s a “bad guy” (nor do I want to completely dismiss this unacceptable behavior) he truly is a sweet heart. I understand what he’s doing isn’t something he should be doing...but.... he has mentioned that it helps him through some things (SIDE NOTE: when we first started dating in high school he had SEVER depression, trust issues, anxiety...etc because of childhood and past relationships) if it helps him is it wrong for me to take it away....? Also I know that a lot of people are going to put down on him immediately or say I’m blind and that the relationship will fail and is doomed etc... I’m just on here looking for honest opinions I’m not saying I don’t want to hear the negative advice/opinions... there’s no way to express or show everything that me and him have been through within a couple of sentences so your only seeing alittle piece of the puzzle I’m just saying please be alittle more constructive than just saying “BREAK UP” “WASTE OF TIME” etc.