Even if you have already married Otis Solicitors says
Relationships and the right to reside in the UK
Your relationship does not give you the right to reside in the UK, however long you have been married and however committed you are to your partner. Some couples struggle with that statement, assuming that British citizens have the right to live with whomever they want in their home country. Whilst a British citizen (or a person with settled status) does have a right to reside, the law says that their husband, wife, civil partner, or partner doesn’t have an automatic right if they are subject to UK immigration controls.
There is a route to UK entry clearance based on your relationship, namely the spouse visa or family visa. However, a marriage certificate or evidence of a relationship isn’t sufficient to secure a spouse visa or partner visa – you have to meet all the eligibility criteria to obtain a spouse visa.
. . .
The route to British citizenship from marriage is quite long and can be complicated depending on your circumstances. Not everyone who marries and comes to live in the UK decides to apply for British citizenship as some think that indefinite leave to remain status is sufficient as it gives them the right to live and work in the UK on an indefinite basis.
On top of that you are not yet married, and (with respect to you and your partner) is there proof that you are the father? There are many, many people who have fallen victim to "visa romances" and I hope you are not one of them. The bottom line is that your feelings for your partner have nothing to do with obtaining residency.
Not needing a visa, isn't the same thing as "not subject to immigration controls".