Can you be in a relationship with a Straight Boy?

So I have became close to a straight boy I work with. Our friendship is confusing as we hug eachother, hand touch, play wrestle, feed eachother food & entertain us as a relationship (making jokes of who is under the thumb)

We then became intimate after a night as they opened up and expressed how they find me irresistible, how I make them question their sexuality, and how they had thought about me. This resulted in us making out and performing mild incomplete oral sex. I asked them if they regretted it the next day which they replied 'well **** happens'.

Our relationship went back to normal same levels of affection etc. It progressed and one time I tried to kiss them sober which they shy fully declined. I then talked to them which they expressed they are confused, think they like girls more though so it was agreed they are fine with it in intoxicated context.

Our relationship then progressed further into sober meeting up cinema trips, giving eachother massages after alone. These massages were half naked and sometimes naked hand on naked areas. But nothing defined as oral.

The level it would now be is innuendos, flirting, a close bond, and we then became intimate again recently doing now everything apart from full intercourse.

Im confused because although I have feelings for them. They are 17 and 'straight' and I'm 22 and comfortable in myself. So I see a lot of me in them so I don't ever ask them or challenge their sexuality. This hurts me though as they make me feel I mean nothing to them. The most I have got from them in discussion to us is that they agree with me that our friendship isn't normal and it is more than that. I also said I was fine with the way it was as long as they would respect me and are not using me which they said they weren't.

Now here is complicated part:
- one minute they are all for me, acting intimate like couples do (cuddling hand holding)
- they will then not communicate with me for a period of time.
- I am best friends with their sister.
- once when confronted about it all they said they would deny it if it ever came out so when I challenge it they get twisted defensive to the point they target me as if I'm potentially threatening
- they text girls and kiss girls and claims he really likes this particular girl.

HOWEVER

I have recently found out from an open gay that they have shared similar experiences with the straight boy also. And they said things to both of us such as how they like the feel of our beards against them. And told them they never experimented with a boy before (they had with me).

What do I do here can anyone give advise?
- Am I best ending this because the age difference is going to make it complicated and I value my friendship with their sister?
- do I challenge them on their sexuality?
- Are they gay or attracted to me? Or are they just a horny straight also? ( we have performed anal oral sex on one another mind you

Any advise would be great. I just want to find someone who will care and commit to me yet I always end up attracting to 'originally' straight men?