So the question is not so much what each side has done but the role you see your new partner taking in the future. If you two see each other as partners in the venture, the split should probably be something like 60-40.
If you see him as someone who will do a bit of front-end dev and then move on to other things, you should give him less.
Although of course, it's always a negotiation and is based very much on intangibles: how much you guys like each other, see yourselves working together in the future, how talented you think he is, i.e. if you think he's a star you should give him a big share of the pie to entice him and keep him involved in the project.
In general though, the guy who started the company (i.e. you) should get a majority of the equity and the people who come later should get equity/options based pretty much on an asymptotic curve with equity on the y axis and time joined on the x axis.
This might be a bit complicated for a side project but you should think about founder options to avoid the "YouTube syndrome" of one founder bailing early and still getting a big payday if it comes to that, and give your partner an incentive to stay involved over the lifespan of the project.
So basically, if you think of him as a full-fledged partner, it should be something like 60-40, and if you see him as less than that it should be something less, and you should think about founder options.