A startup lives in a perpetual state of 'about to fall apart.'
Sometimes you just feel it more acutely than others, based on circumstances and how emotionally volatile you are at the time, in addition to other factors like how important the issue is in terms of actual survival (yours, the startups - which are two different issues, although codependent variables).
Many more issues surface in your short post.
1. You're only 1.5 months in and you've attracted the interest of a prominent angel investor AND your cofounder is meeting his deliverables? That's doing well, not falling apart.
2. You're beginning to feel the strain. That is under your control, and only your control. Look at how you're managing yourself and your energy levels instead of just looking at the business and reaching out to potentially inflate other issues into 'startup ending' crises upon which you could then heap blame when you quit.
If it seems too tough, that's because it IS.
What you have to figure out is whether or not it is too tough for you. Do you want this kind of stress/strain/doubt to surface almost every day for the next 2-7 years?
Are you willing to continue to take on this kind of risk?
Because that's what your startup will require.
Granted, if you're lucky, passionate, and good, and you work your ass off, those will be intermittently interspersed with such blinding moments of success that you'll wonder how you could have possibly considered quitting at any point.
3. Your cofounder relationship seems to be a big potential issue for you. I take it your cofounder is perhaps slightly 'more' technical than you - but could be wrong since you don't state this explicitly.
His risk tolerance is also lower than yours, it seems, as he's maintaining a 'safety' net with the consulting gig on the side.
This can mean many things, but you should perhaps be most worried about this if you're in the CEO/#1 role, as it can indicate a cofounder's lack of trust in your ability to 'drive.'
Falling off the map can happen (I've been guilty of it), but it usually means either you're frantically busy trying to sell, raise funds, etc. or that you've got a life on the other side of the startup which would suffer if you left it, and which you're not quite ready to give up.
It's your job to find out which is going on with your cofounder, preferably before you accept funding. If he's not committed and leaves after funding, and you're nontechnical, you're in a very tricky spot.
You also don't mention the equity split, but if it's 50/50, you've got bigger issues. Maybe the cofounder wants more, maybe he or she thinks she's got 50 % of nothing. If so, it's your job to communicate (and then actually hit deliverables like sales, funding money in the bank, etc) that make the point.
4. Who is going to recruit the CTO? Does the angel know 'a few people?' Does he have a specific person in mind? If so, has he named them, shared the name and a few sentences of this person's experience, and said he'd email or call them by X?
If not, and assurances are vague at best, he's probably relying on you to find someone.
Do not discount the tremendous time, energy, and effort it takes to find this kind of executive as a first time entrepreneur.
Given the other issues, it's challenging but not impossible for you to find a CTO at this point in the company history.
5. Going solo with the project? When you're fearful of him doing the same? Not a great idea. It's a worse indicator that you don't know if he'd pursue the same project independently. That should be what you focus on tomorrow - figuring out who would keep the kids if you divorce.
6. "Another full-time project" will not help you answer whether or not the life of a startup founder is for you. Nothing you've named here (although we're operating on not much data) is a disastrous issue that would require jumping ship.
Reading through the text it sounds like you're feeling itchy, scared, and looking for justification for moving on to the next big thing, before you've even figured out if this one can work.
Side note: Don't assume success in both cases. Assume failure. Your investors will, while hoping you're different.
Not until you've explored the myriad of ways in which you can fail, and confronted these head on with users, competitors, and investors during pitch meetings (ie post launch), will you have any idea of what success and failure will mean for this company.
Work your ass off to learn what you can while working on the one you choose, and you might find a different definition of success than the one with which you began.
And you might be one of the lucky ones with 1x, 3x, etc. exits.