I don't think this is the slightest bit weird and think you are being sensible in getting other's views. It is a most upsetting situation.
I'd like to offer a couple of thoughts.
The first is abut your GF, who has been raising a son since she was around 20, and while you don't say so outright must have been in a relationship that ended somewhere along the line, leaving her a single mum, and with the possibility that she feels uncomfortable starting a new one.
If it had ended badly then trust both of any prospective partner - and herself- is going to be hard for her (and probably for her son too).
Add to that the fact any new partner would have to get on well with her son and you can see it might be a real can of worms.
OK, the other thing of course is that for any successful relationship to work - and last- there has to be affection, trust and understanding between the people involved, a desire to smooth their path and look after them. This understanding does not happen on its own, it needs talk. You have to be able to sort out everything - from money to health, plus feelings.
I guess if it was me I'd see if there was any way to get talking with her, and in the process try to find out her feelings and worries, she already has an idea of yours.
What do you think?