It's essentially a permanent Heroic Offence, only with some additional conditions. Unless those additional conditions are actually going to have a dramatic effect, it's way over powered. Which at this point I think it is. Especially as it would stack with Heroic Offence.
I wouldn't make it +1 to Strength. I'd make it +1 to attack and damage, but only if the characters were fighting adjacent to each other,
or attacking the same target. As the spell gives them a subconscious intuition as to what their companion is doing, allowing them to co-ordinate more effectively.
As a downside I'd make both subjects loose 10 HP permanently. If their companion dies, they can non longer gain the bonuses, and the HP loss remains permanent. A penalty to resist disease/infection may also be appropriate.
With that in mind, I'd adjust the ritual such that they get a deep cut on their chests (Shaking cut hands has been done to death) which never fully heals. The companions can embrace, or not, as you prefer for the ritual. It's magic after all, physical contact doesn't have to be necessary.
I'd also say that it's typical for the companions to supply their own blood to power the spell (Which can be done with the Journeyman level of the Blood Mage Specialization).
I'd make the spell an hour long casting time, to bring it in line with some of the larger ritual like spells (specifically Weather Weaving). TN 16ish, Mana cost at least 7 (essentially 3.5HP per companion, supplemented as necessary by the Mage casting the spell).
I'd also be inclined to give the companions a +1 to all Communication, Perception (Empathy) and Willpower (Morale) tests when interacting with each other. And maybe force a Willpower (Self Discipline) test when the companion drops to 0HP to immediately go to their aid, no matter the dangers. A failed test could result in the character jumping off a cliff to save their fallen comrade for example.

You could tone that idea down, but something similar would be appropriate.
I'd also rename the spell "Blood Bond" just to avoid any gender specifics.
I also like the previously mentioned homing beacon effects.
Or, if you don't want hefty permanent penalties, I'd make it a talent as previously suggested.
Spinning is so much cooler than not spinning.