Just read the number of posts on the divorce / separated board from unmarried women with children who in separation realise they have absolutely no financial rights on separation.
Apart from making a commitment in front of your family & friends….
Marriage can have many financial benefits, including:
Married couples can benefit from tax breaks and exemptions.
Marriage allowance - a non-taxpayer can transfer up to £1,260 of their Personal Allowance to their spouse, reducing their annual tax bill by up to £252
Spouses can transfer assets between them without incurring capital gains tax. If your partner dies - you will have to pay CGT on his share.
Married couples can benefit from reduced inheritance tax rates.
Pension benefits - when your boyfriend dies you aren’t entitled to any of his pension. Married couples - their pension continues after they die
If either spouse doesn't qualify for their own Social Security benefits, they can receive the other spouse's benefits
Married couples may have better access to credit.
Personally I still can’t believe women have children with a man & don’t get married (and I say this as someone never interested in marriage and I didn’t get married until my 50’s). You are leaving yourself in a very risky position if the relationship goes wrong.