I'm thinking of making my boyfriend promise one thing...
What do you want your boyfriend to promise?
That he stops fucking other girls.
It's good to ask partners for such a promise. It's wrong for them to cheat.
It will be my way of being sure that he's being faithful.
Your partner is probably not going to reciprocate that love and is using you for their own desires. It would be better to break it off with them and find someone who automatically knows it is wrong to have relations with other people while dating you.