I caught my BF chatting to guys on the net and I don't know if he hooks up with them or not. He says he wants to keep that side of his sexuality 'Separate' to our love life but I don't want secrets. What do I do? How would I know if he is lying?

Since both of you seem to be bisexual, have you ever thought about trying sex with another bi couple?
Talk to him and make him feel comfortable about his attraction to guys. Then he won't try to hide it from you.

Well, tell him that as long as he has secrets between the two of you that there will be real trust issues in your relationship. Everyone has a personal and private part of their lives in which we like to be alone and apart from our significant others. However, our significant others still should know about it and understand that this time/area is for you. To keep it secret from the other just means that they don't trust you and are not sharing that part of themselves with you. As long as that exists, you won't ever know if he's lying or not.

You have a few choices here:

1) You can tell your boyfriend that if he is going to have an emotional affair behind your back (yes, that is what he is having), then he is granting you the same freedom to have an emotional affair behind his back with whomever you want.

2) You can tell him that unless he is willing to at least open up this aspect of who he is with you, not necessarily to include you, but to share it with you, then you're going to look for someone else who is willing to share all of themselves with you.

3) You can ignore it and hope that he doesn't take it further than what he has, knowing full will that if he does, you and he run the risk of getting STDs, possibly of the incurable kind.

I would decide what you want, sit down with him, talk to him, and figure out a compromise to him having a private life while allowing you to see what he is doing when he does. Maybe he is ashamed of it and he's thinking that you'll think less of him if you knew. Usually that's the case. If he does open up to you, I wouldn't ridicule anything that you discover about his private life and if you want to know more, ask him. Once he sees that you're not a threat to this aspect of what he enjoys, he'll open up to you more, if not possibly include you.