H.W.
Hi L.,
I think the question I would put to you--if you were a friend, asking me for advice-- would be simply "Is your son capable of sleeping by himself?" If the answer was Yes, then I would likely ask you about this statement:"I know where he is and how he is doing, therefore I sleep better." Perhaps it's a benign statement on your part, but I would wonder if there is some anxiety on your part when he's away from you at night, and if so, why-- and what you might do to keep him safe, contained and comfortable so you can sleep well when he's in his own room. (For example, we have a swinging safety gate at the end of the hallway which we close at night; I would wake up if he were trying to open it.)
Those are the two parts I would focus on first. In our culture, yes, bedsharing at this age is rather atypical, and I can understand the concern of your boyfriend's parents. Not that this is a wholly bad thing to be close with our children, however, they should be able to be comfortable separate from us, and we should be comfortable when separated from them.
I do think your concern about your son wanting nothing to do with you in a couple of years is not what I have typically seen from the boys I have cared for and observed, both as a nanny and in my family. Connections are what you make of them. My nephews have all been in their own beds since they were babies and they are all very close to their moms (my sisters) and affectionate in the ways they are comfortable with. Not every kid likes lots of hugs and kisses, but this is more about their temperament, not the parenting.
I would encourage you to separate the co-sleeping issue from the boyfriend issue, being that I wouldn't justify the cosleeping with 'my boyfriend's not there anyway'. I do think that if you are in a relationship with your child's father, that does need work if you are to stay under the same roof. That said, I also think that at five, it would be good for your son's development to have some healthy separation. Please know that I am not against cosleeping--- I coslept with our son until he was three, and after that he slept on our floor on a futon for nearly a year until we moved him into his own room. It took a while for him to get used to it, but we were firm that he was old enough to sleep alone. He's five now and we still make sure he gets lots of snuggles and cuddles from us; he loves for us to snuggle up with him in his own bed in the mornings, now. Attachment isn't about where you sleep, it's about how you parent during the waking hours.
Best of luck.