Fora woman? Yes the biggest commitment, without doubt. She risks her health and economic stability. Even the best MAT pay doesn't make up a full wage, lost pension and lost career progression. Not to mention the fact that having a child means the vast majority of care for a minimum of 18 years, which also impacts on economic prosperity.
For a man however it is very little impact. Pay, assets, economic security and career advancement remain the same. In fact often improved as there is usually a woman who 'takes care' of him to some degree- be that getting his laundry done or have his meals cooked (not to mention doing 70% of housework/life admin) leaving plenty of time for all those lovely 'DP hobbies' we hear so much about .
Having a baby is absolutely NOT a commitment for a man.
The ONLY thing in current UK law that has any impact when it comes to family
Life is MARRIAGE.
With marriage he decides that his strength of feeling for you is so strong - that he is willing to share 'ALL HIS WORLDLY GOODS'. This means ALL the spoils of that economic advantage he gained through your pregnancy , child rearing and housekeeping.
So unless you have your own large private income OP.. Marriage remains the ONLY demonstrable commitment for a man. You only have to read the hundreds of threads on here from woman whose 'DPs' are so desperate to avoid it - especially after kids .
So - OP . He is 'the one eh ? ' ask him if he will get married now. ? Nothing fancy, pop down the registry office in 3 weeks time (you have to give notice) costs about £215 midweek registry with handful of guests or keep it secret with just 2 witnesses and crack on TTC from honeymoon onwards.
You can always have the wedding at a later date when you have time to plan one.
His agreement will be the answer you need. But don't accept 'promises' . Do not TTC until that ring is on your finger .. changes of mind once a partner is pregnant, are common.