I would suggest that you and your S.O. talk about how things will work in this new arrangement. Please don't expect that things will just work out. You two need to lay out a plan of expectations that will work for both of you.
Talk about divison of labor between you and him and YOUR son (when he get old enough to do chores). for example,if you cook, he washes dishes. Or will you wash dishes together. What chores will your son do? Take out trash, mow lawn, what ever. But thats's when he is old enough to do something. He can do small stuff when he turns 4.
Money: According to the experts, how much of your incomes goes towards house hold expenses should be a ratio based on your income and not 50:50, unless you two make the same amount of money. If he makes 2x as much as you, he should contribute 2x as much. You both should have a join account for paying bills, a joint savings account for household emergencies or joint purchases and separate savings.
Debt: Does he have debt or you have debt? How will you pay that off?
Long range plans: buying a house, saving for a house, paying for it. Children, how many, when to have, daycare, verses staying at home. Public school vs private.
Discipline: Since it your child, you need to be the one that does most of the discipling. He should be able to do some, but that's really on you. He will be there to support you.
Growing a family. Since you said that you two plan on being together indefinitely, you'll need to consider family size. If you two have a child together, then of course discipline will have to be consistant between the children. I have seen where the boyfriend will just adore the step-child until they have their own child together and then he starts to favor his child over the step. He will be more critical of the step child than his own, or at least it may be precieved that way.
Please note that what ever plan you two come up with, it will change over time and your family grows and your incomes change. You both need to be willing to renegociate.
When a woman gets married her household chores go up by 8 hours a week and a husband's go down one hour. Even though you are not married, you can expect to do more work as you are auditioning to be his wife. Don't let him just come in and prop his feet up on the table and ask what's for dinner, while you work your butt off at home and at the office. I know chores won't ever be 50:50, but it shouldn't be 98:2 either.
I wish you all the best. Getting married does not mean your relationship will last longer. You two need to have the same vison on the direction you want your family and life to go and be willing to do what you say.