Can I get pregnant this way?

It is not as likely as if he actually cums in you, but yes it can happen. There is also sperm in pre-cum so you could get pregnant from that too.

It is not fair on your boyfriend if you are trying to do this without him knowing though (I am assuming this, since he is not cumming in you), so please discuss it with him. Why do you feel you have to do this rather than just trying to have a baby officially if you really, really want to? Hve you talked about it? Your boyfriend will feel trapped if you just get pregnant, and it will most likely cause a big rift if he finds out you were trying to do it. Having a baby is life changing for both parents, so please realise this and just discuss it. If you really want a baby and he doesn’t then maybe you are not right together and you should conside rmoving on and finding someone who wants a child too.