Feeling lost and alone
Firstly, welcome to the forums.
No one should feel lost and lonely, no one deserves to go through their life like that either. It does sound like your fiancé cares about you, I know it can be overshadowed when you are alone with your thoughts and may overthink certain things. Have you thought about joining some sort of a mothers group to get to know other mothers and can possibly make friends that way?
My other thought is have you ever spoken to a GP about how you are feeling and seeing if possibly speaking to a psychologist may benefit you as well?
My best for you,
My other concern is that even though you can talk with your fiance about what you need to, does mean that there will be times when the two of you do have an argument or disagreement which then leaves you with no one you can contact and no one who can help you discuss what problem there maybe, so that's when you are going to feel the most loneliness.
No I don't think he has much over you because remember it goes both ways, because there would be times when you do or want to push him away, so the communication does go both ways, the only problem is that you missing other g/friends.
Although your children are young they must want to go and play on the swings at the park, no different than what other children want to do, so other mums must be there and could quite possibly be in exactly the situation as you are, waiting and hoping that another has mum has the confidence to say 'hello', and if this happens then it's a great chance to invite them back to your place for a coffee or vice-versa, and it's not too hard to say hi, especially if that's what you really want to do and make some friends.
I realise that at the moment you're about to give birth to another baby which may stall this for a few weeks, but perhaps you could be in a double room at the hospital, so start up a r/ship by talking with the other mum. Geoff. x