My 7. Y.O. son keeps crawling in my bed at night

I have a 7 YO son and a 3 (almost 4) daughter. For the better part of a month my son has been waking up between 2 and 4 a.m. and crawling in my bed. The first time, I thought "oh well...". He would occassionaly do that, perhaps once a month or two months, and I figured he just had an off night. The second night I didn't even hear him and I woke up and he was sleeping next to me. Since then, it's been almost every night--at best, every other night--that he's woken up and tried to crawl into my bed. I am kind of at a loss. It seems he regresses to "I'm scared" (in a very, tired/whiney voice in which you know there's no rational conversation at this hour about fears), although I suspect that while that may in some part be a small part of the reason, he is largely waking up because he knows there's a good possibility that he can manage to get in my bed for awhile, if not the whole night (before my daughter turned three, she would do this almost every night--wake up in the middle of the night, simply out of habit--and waddle her way down to my bed). He's never had this problem before...if ever it were two nights in a row, I could just place him back in his bed on the second night and tell him "Daddy's bed is for daddy. Your bed is for you" and he wouldn't rinse and repeat the behavior.A bit of background. I'm a single father, full time. When my kids were 3.5 and 6 months, respectively, their mother passed away suddenly. Stability and consistency aren't entirely luxuries we have afforded, though I feel I've done a pretty good job overall in trying to be emotionally present, acknowledge their feelings, enact consistent discipline. I'm a million miles away from perfect, but I don't think this issue has to do with not getting the needed attention or verbal affirmation (even if I sometimes have to be more segmented about it--two of them, one of me). My son is also increasingly a hyper-sensitive child, I believe. He's definitely ADHD--his mother, uncles, and grandfather has it. He's not my biological son, so I'm not 100% sure what psychological stuff exists on that side (he's fully adopted by myself though). But it seems that this middle of the night stuff has happened in conjunction with an increase in his sensitivity levels. If he bumps his shoulder (as long as there's nothing more stimulating), he's liable to cry about it (or, at the very least, insist he needs to tell me about it). He's got a ton of energy and can be motivated to be an awesome helper but other times it's an incredible struggle to get him to do anything much at all without him taking it as personal rejection. Hence, I don't want to turn the middle of the night stuff into "I don't want you to be here" but I can't have me and my kids sharing the same bed. They have their own and I can't keep waking up every night to put a seven year old boy back in his, all the time worrying about the level of self-rejection he's taking it to be.Okay--sorry this was a bit long. Our world's a bit of a mess and as someone who's decently informed about human psychology, I also understand a lot of this is pretty multi-dimensional. That said, he's a 7 y.o. boy and I'm at a loss for what to do here.Oh...and yes...he has a nightlight, we say our prayers, and we avoid scary stories/shows, etc. via /r/Parenting http://ift.tt/2bB2CnW