I have been seeing my boyfriend for 6 months. He has 19 and 14 year old sons. I have 18, 15, sons and 12 year old daughter. We were high school mates back 25 years ago. Ok so.. Every since his ex wife left and they divorced over a year ago, the 14 year old son sleeps every night with his dad. He has his own room and bed, but only will sleep in bed with his dad and dad allows it.. Even at times encourages it. I think this is rather strange. I have only allowed my children when they were very young to sleep with me and only when they were sick. How long is long enough and how should I approach this or should I.
Please help me I need advice.

It doesn't sound strange in light of his mother leaving and the divorce.

It sounds like the boy is very insecure and very much needs to be close to his dad.

I would tactfully suggest to dad that maybe the 14 year old needs to see a psychiatrist about the divorce.

Other than that, no I personally don't see an actual PROBLEM with it.

When he stays with his mother for a night or two he sleeps by himself.

Its possible he feels that his mother is at fault. He is old enough to 'understand' what is happening, but at the same time, NOT old enough to fully grasp exactly what is going on.

He may see her as 'the bad guy' who split the family up.

And in turn, feels safer with dad, safer to be more vulnerable and let his feelings take course, instead of hiding it and trying to be a 'man'

I'm just suggesting. I don't know the whole situation.