Go ahead and make as many plans to do stuff with your friends and alone as you want. Let him know in advance what your week-end plans are (when your reasonably can without bombarding him with you diary). And then it's up to him whether he joins you or not.
This will change the relationship dynamic to a better one. To one where you are no longer at his beck and call all the time. One where he sees that you are making the most of your time and that your time is valuable to you. And that therefore he has to compete for your time.
Of course, when you do get together, aim to make that just as special or more special than it's ever been with him.
Your boyfriend does come as a package with his existing children. I get the impression that you are realistic about this. But it is worth reminding yourself from time to time that his children will always have a high priority (and quite rightly so).
On the one hand you don't want to beg him or nag him to see you. On the other you could suggest specific events, activities, themes. Such as going away to a hotel with a swimming pool for the week-end on a cheapo deal. Or walkng a section of South West Coast Path.
What's normal and what's unusual are not important in a relationship. It's what works best for the 2 of you that counts
In fact, what most couples do is pretty dumb. Hence the high divorce figures. There is an art to keeping long term relationships fresh and worth continuing. It's an art that many people never master.
At some point it makes sense to move in with your boyfriend. Do you think that's realistically on the cards? And do you think you'd get on really well if you did?