In the event of you separating, currently you would only be entitled to CMS. If you know his income you could work it out. Could you live on this or would you have to rely on benefits?;
This is because you have effectively been renting, whilst living in your boyfriends house.
If you pay towards the mortgage you may have a claim BUT you would need to go to court which isn't cheap so potentially the benefit would be outweighed by solicitor fees.
If you pay towards the mortgage and signed a Deed of Trust you would have some legal basis to equity in the property.
If you married, the finances would depend on many factors, how long married, how old you both were, opportunity for you to earn and support yourself etc. However marriage would definitely provide a legal framework to enable you to have "rights" to some of your boyfriends assets, such as equity, savings, pension that he is currently building up for HIMSELF.
At present you are in the weakest position. Make sure you are paying whatever you can into a pension. Prioritise that, salary sacrifice additional contributions, as too many women will be elderly and very poor as a result of cohabiting and not building up a pension.